It is theorized that all of the Earth’s land masses were once joined together in a single continent known as ‘Pangaea’ which, around 180 million years ago, split in two – Laurasia in the north and Gondwanaland in the south.As time (a lot of it!) passed, these two land masses split apart several more times into the continents we now know. When one considers that the slate deposits that run up the east coast of North America are virtually identical to those found in Wales, it seems like a plausible explanation.